FIGS. 30 and 31 illustrate conventional thermal printheads. The thermal printhead X1 includes an insulating substrate 90, a glaze layer 91, a resistor 92, electrodes 93a, 93b, and a protection layer 94 laminated in the mentioned order (see Patent Document 1, for example). The resistor 92 includes a heating portion 92a arranged between the electrodes 93a, 93b. The heating portion 92a generates heat which enables printing on a thermal recording medium.
In manufacturing the thermal printhead X1, the electrodes 93a, 93b are formed after the formation of the resistor 92. Formation of the electrodes 93a, 93b is performed by printing and then baking resinate gold paste on the resistor 92. Due to the heat for the baking, the resistor 92 may be oxidized into alteration.
To solve this problem, the resistor 92 and the electrodes 93a, 93b of the thermal printhead X2 shown in FIG. 31 are laminated to each other in an order different from the thermal printhead X1 shown in FIG. 30. With such arrangement, when forming the electrodes 93a, 93b, the resistor 92 is not yet formed. Thus, the resistor 92 is prevented from being oxidized due to the baking step of the electrodes 93a, 93b. 
However, the thermal printhead X2 shown in FIG. 31 still has room for improvement as described below.
First, the electrodes 93a, 93b provide a surface level difference H relative to the glaze layer 91, by the thickness of the electrodes 93a, 93b. The resistor 92 is bent through a sharp angle at the portions with the surface level difference H. It is difficult to properly form the resistor 92 with a bend at a sharp angle. Further, the resistor 92 is likely to be disconnected at the bent portions.
Second, the heating portion 92a of the resistor 92 is arranged at a low portion between the electrodes 93a, 93b. Thus, when a thermal recording medium is arranged on the protection layer for printing, a distance between the thermal recording medium and the heating portion 92a is relatively large. This lowers the heat transfer efficiency from the resistor 92a to the thermal recording medium. As a result, the print density is lowered and thus poses difficulty in the high-quality printing as well as the high-speed printing.
Third, the surface of the protection layer 94 has irregularities because of the arrangement of the electrodes 93a, 93b and the resistor 92. In the irregularities, there is a tendency of accumulation of ink of an ink ribbon for thermal recording or of paper particles of thermal paper. Further, transfer of the thermal recoding medium cannot be performed smoothly in contact with the surface of the protection layer 94.